Rectifying apparatus



Feb. 24, 1931. J. J. FITZ PATRICK 1,794,283

RECTIFYING APPARATUS Filed June 25, 1929 ELECTRON/CALL Y ACTIVE MATERIAL a Imvefitor:

James J.Titz Patrick,

His Attorney.

Patented Feb. 24, 1931 UNTED STATES Aren't oFFicE JAMES J. FITZ PATRICK, OF MARBLEHEAD, MASSACHUSETTS, ASSIlZG-NOIB. '1'0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK BECTIBYING Application filed June 25,

The present invention relates to electrical translating apparatus and more particularly to thermionic devices for converting alternating current into direct current.

Objects of the invention are to provide a rectifier capable of delivering a large power output having a rugged construction and a relatively long operating life. These and other objects are attained in brief by employing in the device a cathode, either directly or indirectly heated and coated with an electronically active material, the cathode being enclosed in a shield having suitable discharge openings and immersed in an ionizing medium. The invention will be better understood when reference is made to the following description and accompanying drawing in which Fig. 1 shows in perspective, a view of the improved rectifier, while Fig. 2 is a view,

somewhat enlarged, of the details of the electrode construction and arrangement.

Referring to Fig. 1, numeral 1 designates an evacuated envelope terminating in a press 2 and secured to a base 3 in which four contact pins 4 are mounted. The anodes 5, of which there are two in the case of a full-wave rectifier and one in the case of a half-wave rectifier, may take the form of a cylinder hollowed out at the top to increase the heat radiating surface and constituted preferably of rod carbon, graphite, nickel or the like. The anodes are supported from the press 2 by means of stiff wires or conductors 6, which are carried through the stem to connect with a pair of contact pins 4. Protective sleeves 7,

of glass or other insulating material are fitted over the anode conductors at the place where they emerge from the press to prevent the wires from being pitted during operation of the tube and to ensure insulation at this place. The cathode may comprise a hollow cylinder 8 (Fig. 2) preferably of nlckel, arranged equidistantly between the anodes 5, and shown somewhat higher in elevation,

altho if desired, this member may be sup- APPARATUS 1929. Serial No. 873,632.

ported at the same height as the anodes by means of a wire support 9 to which the cylinder is affixed by clamp sleeves 10. The cathode 8 is heated by means of a heater element 11, the upper end of which is suspended from an extension of the cathode support 9, the lower end being atfixed to a conductor 12; if desired the element 11 may constitute the cathode and the cylinder 8 be omitted. The wires 9 and 12 are'extended through the stem and connected to the remaining pair of contact pins. The outer surface of the cylinder 8 is preferably coated in any satisfactory manner with an electronically active material, for example barium. When barium is employed, the material conveniently may be applied as a paste of barium carbonate (BaCO and a suitable binder, and the cathode heated to a temperature (about 1200 C.) by a high frequency coil, a bombarding discharge or in any other suitable manner, at which the active material is observed to flow over the surface to form a transparent, uniform layer. The cathode is completely enclosed on all sides except the bottom by a shield 13 which is supported by means of cars 14 engaging with oppositely disposed wires 15, one of which is fused in the press and the other affixed to the cathode support wire by a horizontally extending conductor 16. The shield 13 may be fabricated of thin sheet stock pref erably nickel and is conveniently shaped as a rectangle by bending the metal at the corners. Tabs are provided at the top of the shield which fold over each other so as completely to close the upper end. The shield extends a considerable distance beyond the edge of the electrodes nearer the stem in order to preclude discharge through the open end. When in position, the respective pairs of sides of the shield are in planes normal to and parallel with the plane of the electrodes, the interior dimensions being such as to allow the shield to fit over the cathode with the minimum clearance without danger of contact. .0

There are two oppositely disposed slits or openings 17 of any suitable shape but shown as taking the form of an elongated rectangle cut in the sides of the shield and positioned in the plane of the electrodes, havin an area sufiicient to pass the discharge without undue voltage dro As illustrated, the various elements wit in the tube are so arran ed that a vertical plane will bisect the an es, the shield, slits and the cathode although it will be understood that variations of this arrangement come within the purview of my invention.

The envelope after evacuation in the wellunderstood manner including thorough denudation of gas occluded in the electrodes, may be filled with an inert gas, such as argon, at a pressure between 80 and 200 microns Hg. and in addition a drop of mercury (not shown) is provided as an additional sour ce of positive ions with which to reduce the voltage drop in the tube;

The energy to be rectified is usually supplied through a suitable transformer (not shown) the primary of which may be connected to the ordinary alternating current house supply. A tube of this character is capable of passing a relatively large current at a voltage suitable for battery charging devices or. as a substitute for motor-generator sets, also for energizing filaments of radio tubes and for similar purposes. The discharge between one anode and the cathode during each half of the alternating current cycle takes on the appearance of an arc, the current stream being characterized by a low voltage drop and by a flat or negative volt ampere characteristic depending upon the configuration of the electrodes and the gas pressure employed. The current stream concentrates as a glow about each of the slits 17 inasmuch as these openings offer the only path between electrodes for the discharge. Obviously, in directing the arc stream, the shape, size and position of the slits distinctly affect the operating characteristics and the life of the tube. The use of the shield greatly improves the operation and increases the tube life; in general, the smaller the size of the slit in the shield for a given voltage drop, the more favorable will these factors become. The proper shape, size and position of the slits depend upon many considerations, including the gas and vapor pressures, the voltage employed, configuration of and distance between electrodes, and is best determined by test under operating conditions. A rectangular slit of a length approximately 8 m. m. and 1.75 m. m. wide has given satisfactory results in a tube such as that illustrated and with the gas pressures mentioned hereinbe-fore. The shield apparently performs the functions of reflecting the barium or other electronically active material which evaporates from the cathode, back to this member in addition to reventing the contamination of the cathode y material removed from the anode by bombardment. Moreover, inasmuch as the shield is at cathode potential and itis situated fairly close to the anodes, the bombarding effect of the electronic discharge on the anodes and leads is much less than in the absence of the shield. As a practical example of the efiicacy of the slitted shield, a tube not equipped with this member was run for 450 hours and the anodes, also leads, were found to be pitted and badly worn away by etching as a result of the electronic discharge. However, a tube equipped with a shield has operated over a period more than twice as long without showing any appreciable wear of the anode and its lead. In addition to preventing excessive electron bombardment of the anodes the shield also offers a substantial protection to the cathode and heater members from ion bombardment without unfavorably affecting the potential gradient between the electrodes. The advantage of shielding the oathode from ion bombardment is particularly beneficial in the case of cathode surfaces coated with electronically active material such as barium or when the cathode takes the form of a directly heated filament of fragile construction. It is apparent that the gas and vapor are offered free access to the interior of the shield by the open end thereof in addition to the path afforded by the slits. The

length of the shield is such as to preclude the formation of a current stream at the bottom of this member thereby vesting solely in the slits, the functions of directing and regulating the character of the arc glow discharge. lVhatever be the correct theory involved as pertaining to the operation of the apertured shield, it has been found that the life of a full-wave rectifier of the type described has been materially increased when the shield is provided and also that the tube rectifying characteristics have been substantially improved.

Broader aspects of the invention are claimed in the Simon and Bareiss application Serial No. 280,877, filed May 26, 1928, entitled Electric rectifiers and assigned to the same assignee as the present application.

What I claim as new and desire to secure by- Letters Patent of the United States, is:

1. A rectifier comprising an envelope containing a cathode and a pair of anodes, said anodes being mounted on opposite sides of the cathode, an ionizable medium in the envelope at a pressure sufficiently high to support an arc-like discharge, a shield mounted about the cathode and adapted to be maintained at a fixed potential with respect thereto, said shield being closed at one end and having a plurality of discharge openings in the plane common to the cathode and anodes.

2. A rectifier comprising an envelope containing an ionizable medium at a pressure s'ufiiciently high to support an arc-like discharge, a plurality of anodes and a cathode, said cathode being coated with an electron ically active substance and subject to contamination by material sputtered from the anode, means for shielding the cathode from positive ion bombardment and the anode from electron bombardment, said means comprising a hollow metallic member adapted to be electrically charged and enclosing the cathode except for a plurality of oppositely disposed relatively small discharge openings therefrom, said means comprising a hollow "metallic member enclosing the cathode and electrically connected thereto, said member being closed at one end and open at the other end, also of suflicient length to preclude discharge through the open end, said member having a plurality of discharge openings for current to pass between the electrodes.

In witness whereof, Ihave hereunto set my hand this twenty first day of June, 1929.

JAMES J. FITZ PATRICK.

in the plane of the cathode and anode members,

3. A rectifier comprising an envelope containing an ionizable medium ata pressure sufficiently high to support an arc-like discharge, a plurality of anodes and a cathode of elongated dimension, said cathode being coated with an electronically active substance and subject to contamination by material sputtered from the anode and means for shielding the cathode from positive ion bombardment and the anode from electron bombardment, said means comprising a hollow metallic member of elongated dimension connected to the cathode and enclosing the latter except for a plurality of small discharge openings in the plane of the cathode and anode members, said openings being of a rectangular elongated shape having the long dimension in the direction of the common plane and of a length less than that of the hollow,

to the cathode, material evaporated there- 'from, sald means comprising a hollow metallic member enclosing the cathode and connected thereto, said member being closed at one end and open at the other end and of sufficient length to preclude discharge through the open end, said member having a plurality of oppositely disposed discharge openings in the plane of the anodes and cathode.

A. rectifier comprising an envelope contaming an ionizable medium at a pressure sufliciently high to sup ort an arc-like discharge, a plurality o anodes, a cathode coated with alkaline earth material, the cathode being subject to contamination by ma terial sputtered from the anode and also subject to loss of the alkaline earth material by evaporation, means for shielding the cathode from positive ion bombardment and for returning to the cathode, material evaporated 

